Moving biodiesel in the pipeline: sequencing matters

The ability to move biodiesel in pipelines versus truck or rail is considered essential to lower costs and advance biodiesel into the mainstream, but contamination of jet fuel with fatty acid methyl esters (FAME) shipped in the same line has impeded progress. The ASTM jet fuel spec has traditionally been unforgiving, only allowing 5 parts per million FAME concentration. Years of work testing higher limits is paying off though, as ASTM recently approved increasing the allowable concentration of trace FAME in jet fuel from 5 to 50 ppm—an action that awaits official publication in the updated jet fuel standard.

Rod Woodford, manager of shipper relations and product quality for Explorer Pipeline, spoke in January at the National Biodiesel Conference & Expo in Fort Worth, Texas, about testing his company conducted in its pipeline, which extends from Houston to Chicago in 10- to 28-inch diameter lines.

Woodford said the company tested movement of 5 percent biodiesel in the 10-inch portion of the pipe that runs from Houston to Dallas with various batch sequencing to better understand the trailback issue. This line moves 2,800 barrels per hour and has a line fill of 144,000 barrels. It’s 266 miles long and product travels at 4 miles per hour. Transit time from Houston to Dallas in the 10-inch pipe is five days. Explorer Pipeline does not ship jet fuel in this segment.

Woodford said trailback—residual amounts of biodiesel found in product shipped subsequently in the pipeline—occurs because FAME sticks to the sidewalls, dead legs, valves and pumps of a pipeline system. When subsequent product is moved through the line, it can pick up trace amounts of biodiesel left behind. For jet fuel, this can make the product out of specification.

First, Woodford said, the company ran a load of B5 biodiesel followed directly by neat diesel, or diesel fuel without the presence of biodiesel. The test showed that FAME contamination was evident well into the neat diesel volume that followed the B5 shipment. While ASTM D975, the diesel fuel spec, allows for up to 5 percent biodiesel, the neat diesel was used as a surrogate for jet fuel in the test. Woodford said the presence of trace FAME far into the diesel fuel volume that followed the B5 shipment in the pipeline segment from Houston to Dallas made him and his colleagues wonder how big a shipment of neat diesel was needed to mitigate the issue.

In the next test of batch sequencing, Explorer Pipeline moved B5 through the same line followed by gasoline. The test proved gasoline is very effective in reducing trailback of FAME in the pipeline, Woodford said, adding that lighter fuels such as gasoline are better at removing trace amounts of FAME from the pipeline sidewalls, dead legs, valves and pumps.

“This test told us there’s a way to confidently move B5 in the same pipeline as jet fuel,” he said. “We just have to get the sequencing right.”

Woodford said Explorer Pipeline is now seeking partners and shippers to trial product movement in the pipeline in a presumed sequence of B5, gasoline and jet fuel, but he admitted they were not yet sure whether higher blends of biodiesel such as B20 and a larger pipeline diameter would yield results similar to their initial findings.

“We’re excited about the potential to integrate [biodiesel] on a regular basis,” Woodford said. “Incorporating B5 into the pipeline is one more step in normalizing it.” Ultimately, he said, being able to ship greater volumes of biodiesel through the nation’s pipeline network would positively affect margins and relieve busy terminals of heavy truck traffic.